Senior Mechanical Engineer (Valves & Components)

About this role

ABOUT ENDURANCE

Endurance is building the world's first modular subsea geothermal power plants, converting vast thermal resources under the ocean into gigawatts of baseload power. Backed by Founders Fund, Felicis, First Round Capital, and Point72 Ventures, our founding team includes veterans from SpaceX, Helion, Blue Origin, and Apple. We have completed multiple deep-ocean deployments to subsea volcanoes and are launching a long-term demonstration project this fall. By leveraging modular design, manufacturing scale, efficient drilling, and latent cooling on the seafloor, we are pioneering a new category of energy that outperforms traditional sources on environmental impact, deployment speed, and cost.

The Role

Our seafloor power plants move 250-350 °C geothermal fluid through a closed loop 1-3 km underwater, surrounded by near-freezing seawater at 100-300 bar. Every valve, seal, fitting, compensator, and filter in that loop has to hold hot, corrosive, scaling fluid on one side and the deep ocean on the other, for years, with no one able to service it. Nobody makes these parts off the shelf. We design, build, test, and deploy them.

In this role you will focus on the fluid components of the plant: isolation, check, control, and relief valves; seats and seals; fittings, manifolds, and compensators; filters and strainers. You will share that scope with a few other engineers, and specific components will be yours end to end. Most of the work is clean-sheet design. You will size seats and springs, choose materials that survive chlorides, sulfides, and silica scaling at temperature, and build the hot-fluid test rigs that qualify your hardware. This is a natural fit for someone who has designed propulsion valves and wants to apply that experience to a hotter fluid, a higher ambient pressure, and a much longer mission.

Your First Year

Help deliver the fluid-component set for our first commercial system, the first subsea geothermal plant to put power on a grid: designed, built, qualified in our own test cells, and operating on the seafloor. The components you own become the baseline for the plants that follow.

How We Work

Our mechanical engineering team is a small group of senior and principal engineers who split the plant's hardware between them. Each engineer owns their hardware end to end: requirements, design, drawings, build, test, and deployment. Principal engineers own the plant architecture, and you will be part of those decisions. We are looking for people who have built hardware, debugged it in the lab or the field, and want to own the result.

Responsibilities

• Own specific fluid components in the working-fluid loop from requirements through design, qualification, and field performance

• Design valves (isolation, check, control, relief) and sealing systems for 250-350 °C fluid with 100-300 bar external seawater pressure

• Select and qualify materials for hot chloride, sulfide, and silica-scaling environments: nickel alloys, duplex stainless steels, titanium, coatings, and hardfacing

• Perform first-principles flow, thermal, and structural analysis: seat loads at temperature, thermal growth and tolerance stacks, pressure-boundary margins, and fatigue

• Design and build hot-fluid test rigs; run pressure, endurance, leak, thermal-cycling, and corrosion tests to qualify components

• Lead root-cause investigations on test and field hardware and implement corrective actions

• Define interfaces with the actuators and pressure boundaries owned by your peers

• Work directly with machine shops and specialty suppliers on tight-tolerance parts in exotic alloys

• Contribute to plant-level fluid-system architecture decisions alongside our principal engineers

• Create detailed 3D CAD models, drawings, and tolerance stacks

Basic Qualifications

• Bachelor's degree in mechanical engineering, aerospace engineering, or a related engineering discipline

• 6+ years of professional experience designing, testing, or manufacturing fluid-control hardware (valves, regulators, seals, pumps, or similar) for demanding environments

• Ownership of at least one fluid component from concept through qualification and fielded use

Preferred Skills and Experience

• Experience designing propulsion valves or flow-control devices for rocket engines or feed systems (cryogenic, hot-gas, or high-pressure)

• Equivalent depth in subsea oil & gas components (trees, chokes, API 17D/6A), high- temperature steam or geothermal hardware, or nuclear-grade pressure-boundary components

• Strong understanding of seal and seat design, leakage physics, and seal behavior across large temperature ranges

• Strong fundamentals in solid mechanics, fluid dynamics, heat transfer, and materials; comfortable with hand calculations and FEA

• Experience designing and running qualification and acceptance tests and analyzing the results

• Hands-on experience with GD&T, design for manufacture in hard-to-machine alloys, and time in a machine shop and test cell

• Experience at a small or fast-moving hardware organization, where you had to make good engineering decisions with incomplete information and limited resources

• A track record of taking on increasing responsibility and delivering something difficult early in your career

• Experience on an engineering competition team (Formula SAE, Baja SAE, RoboSub, rocketry, or similar) or an equivalent self-directed hardware project

COMPENSATION, BENEFITS, & PERKS

As a pre-revenue startup, Endurance Energy offers competitive base salaries and generous equity packages for full-time employees. Final base salary will be determined by an array of factors including internal equity, job-related knowledge, skills, and work experience.

A key aspect of our compensation philosophy is that value creation should be aligned with rewards. Right now this means equity is a significant portion of every full-time employee's compensation. As the company matures, there will be continued…